Many medical procedures require use of a cannula, through which one or more medical instruments are inserted into a patient and then removed from the patient.
For example, in a variety of laparoscopic medical procedures (including laparoscopic hernia repair), a cannula is positioned with its distal end inside the patient and its proximal end outside the patient, and one or more medical instruments are inserted through the cannula into the patient. For example, each of a sequence of instruments (including an endoscope) can be inserted through the cannula into the patient and then withdrawn (in the opposite direction) out from the patient and cannula.
During many such procedures, it is necessary to maintain an insufflated working space within the patient (by maintaining insufflating gas at sufficiently high pressure in the working space) while the distal end of the cannula extends into the working space. For use during these procedures, the cannula must be provided with a seal or seals for preventing undesired fluid escape from within the patient out through the cannula. The term "fluid" is used herein to denote either a gas or a liquid. One such seal (denoted herein as a "fluid" seal) prevents fluid escape from the cannula when no instrument occupies the cannula's channel. A fluid seal is implemented as a flapper valve, duckbill valve, or other valve, which is biased in a closed position at times when no instrument occupies the cannula's channel to provide a fluid seal preventing fluid flow through the channel at such times. When the distal end of an instrument is inserted into the channel and the instrument is advanced through the channel toward the patient, the instrument opens the fluid seal (e.g., by displacing the flexible slits of a duckbill valve or displacing the trap door of a flapper valve).
Typically also, an additional seal (sometimes denoted herein as an "instrument seal") is employed in a cannula to provide a fluid seal around the instrument's outer periphery, to prevent fluid flow through the space between the instrument and the wall of the channel.
Typical prior art cannulae have had a complicated design with a built-in fluid seal and usually also an instrument seal. Such cannulae were expensive to manufacture. They were also difficult to clean after use, since contaminants often coated or became lodged in those small valve and seal parts which were in fluid communication with the cannula channel or the instrument inserted through the cannula. Often, the design of such a cannula was further complicated by the need for a mechanical linkage for manually controlling the flapper valve (e.g., to enable sufficient manual force to be applied on the linkage by a user to open the flapper valve in cases where sufficient force could not be exerted directly on the valve by an instrument without damaging the valve, another component of the cannula, or the instrument, or to enable the flapper valve to be opened for cleaning or the like).
For example, U.S. Pat. No. 5,104,383, issued Apr. 14, 1992, describes a cannula having a built-in flapper valve, and a removable "adaptor seal" which provides an instrument seal for an instrument of a first diameter. The adaptor seal can be removed and replaced by another adaptor seal which provides an instrument seal for an instrument of a second diameter.
For another example, U.S. Pat. No. 5,385,560, issued Jan. 31, 1995, describes a cannula having a built-in flapper valve, and a built-in instrument seal for an instrument having a relatively large diameter. A "reducer" member snaps on the end of the cannula, to provide an instrument seal for an instrument (having a relatively small diameter) which may be inserted through the cannula.
For another example, U.S. Pat. No. 5,290,245, issued Mar. 1, 1994, describes a cannula having several threaded portions which are assembled by being screwed together. The cannula includes a flapper valve mounted on one of the portions and an instrument seal mounted on another of the portions.
It has been proposed to design a cannula to have a distal portion (for insertion in a patient), and a proximal portion which is removably attachable to the first portion and which includes a fluid seal. For example, U.S. Pat. No. 5,460,615, issued Oct. 24, 1995 to Karl Storz, discloses (with reference to FIGS. 4-7) a cannula having a distal portion (with a trocar sleeve and a valve housing) and a proximal portion (with a flapper valve, a first instrument seal, and a second instrument seal attached by a tether to the first instrument seal). A bayonet closure is provided for removably attaching the proximal portion to the distal portion. However, the proximal portion has a complicated structure, it would be expensive to manufacture, and it is not intended to be used once and then discarded.
It had not been known until the present invention how to design a cannula assembly with a simple reusable cannula, and a simple disposable seal (including both a flapper valve fluid seal and at least one instrument seal) which can be snapped onto the cannula and then readily removed after use.